Download genetic similarity theory, ethnocentrism, and group selection

Rushton, J. P. (1998). Genetic similarity theory,
ethnocentrism, and group selection.
In I. Eibl-Eibesfeldt & F.K. Salter (Eds.),
Indoctrinabilitv. warfare, and ideology: Evolutionary
perspectives (pp. 369-388). Oxford: Berghahn Books.
CHAPTER SEVENTEEN
GENETIC SIMILARITY THEORY,
ETHNOCENTRISM, AND GROUP
SELECTION
/. Philippe Rushton
Introduction
Genetic similarity theory, an extension of the kin-selection theory
of altruism, postulates that people detect genetic similarity in others ("nonkin" as well as "kin") in order to provide mutually supportive environments, such as marriage, friendship, and social
groups. In line with prediction, studies using blood antigens and
heritabilities reveal that sexually interacting couples and samesex friendships are based partly on genetic similarity (Rushton
1989a; 1995). As such, a new theory of attraction and friendship is
constituted, and the conditions for the evolution of human altruism are enhanced. Genetically biased preferences are not limited
to social partners but extend to adopting other cultural practices
maximally compatible with genotypes. Ethnocentrism and patriotism may be fitness-enhancing mechanisms that enable group
selection to occur.
Choosing social partners is among the most important decisions individuals make affecting their social environment. The
tendency is to choose similarity. For example, spouses tend to
resemble each other in such characteristics as age, ethnic back-
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ground, socioeconomic status, physical attractiveness, religion,
social attitudes, level of education, family size and structure, intelligence, and personality. The median assortative mating coefficient for standardized intelligence tests averages about 0.35.
Correlations tend to be higher for opinions, attitudes, and values
(0.40 to 0.70) and lower for personality traits, personal habits, and
physical features (0.02 to 0.30).
Most explanations of the role of similarity in human relationships focus on immediate, environmental effects, for example,
their reinforcement value. Recent analyses, however, suggest that
genetic influences may also be involved. According to "genetic
similarity theory," genetic likeness exerts subtle effects on a variety of relationships and has implications for the study of social
behavior in small groups and even in large ones, both national
and international. The main purpose of genetic similarity-seeking
is to enhance altruism.
The Paradox of Altruism
As recognized by Darwin (1871), altruism represents a paradox for
theories of evolution: How could altruism evolve through "survival of the fittest" when, on the face of it, altruistic behavior
diminishes personal fitness? If the most altruistic members of a
group sacrifice themselves for others, they run the risk of leaving
fewer offspring to pass on the very genes that govern the altruistic behavior. Hence, altruism would be selected against, and selfishness would be selected for.
The resolution of the paradox of altruism is one of the triumphs
that led to the new synthesis called sociobiology. By a process
known as kin selection, individuals can optimize their inclusive
fitness rather than only their individual fitness by increasing the
production of successful offspring by both themselves and their
genetic relatives (Hamilton 1964). According to this view, the unit
of analysis for evolutionary selection is not the individual organism but its genes. Genes are what survive and are passed on, and
some of the same genes will be found not only in direct offspring
but in siblings, cousins, and nephews and nieces, as well as more
distant kin. If an animal sacrifices its life for its siblings' offspring,
it ensures the survival of common genes because, by common
descent, it shares 50 percent of its distinct genes with each sibling
and 25 percent with each sibling's offspring.
Genetic Similarity Theory I 371
From an evolutionary perspective, altruism is a means of helping genes to propagate. By being most altruistic to those with
whom we share genes, we help copies of our own genes to replicate. This makes "altruism" ultimately "selfish" in purpose. Promulgated in the context of animal behavior, this idea became
known as "kin selection" and provided a conceptual breakthrough by redefining the unit of analysis away from the individual organism to his or her genes, for it is these that survive and are
passed on. Another way sociobiologists have suggested that altruism could evolve is through reciprocity. Here there is no need for
genetic relatedness; performing an altruistic act need only lead to
an altruistic act in return.
Detecting Genetic Similarity
In order to pursue a strategy of directing altruism toward kin, the
organism must be able to recognize degrees of relatedness. There
is clearly no such thing as "genetic extrasensory perception." For
individuals to direct altruism selectively to genetically similar
individuals, they must respond to phenotypic cues. This is typically accomplished by detecting similarities between self and others in physical and behavioral cues. Four processes have been
suggested by which animals recognize relatives: (1) innate feature
detectors, (2) matching on appearance, (3) familiarity, and (4) location. They are not mutually exclusive. If there are evolutionary
advantages to be gained from the ability to detect genetic similarity, all the mechanisms may be operative.
Innate feature detectors. Individuals may have "recognition alleles" that control the development of innate mechanisms allowing
them to detect genetic similarity in strangers. Dawkins (1976) suggested a thought experiment to illustrate how this could come
about, known as the "green beard effect." In this, a gene has two
effects: it causes individuals who have it (1) to grow a green beard
and (2) to behave altruistically toward green-bearded individuals.
The green beard serves as a recognition cue for the altruism gene.
Altruism could therefore occur without the need for individuals to
be directly related.
Matching on appearance. The individual may be genetically
guided to learn its own phenotype, or those of its close kin, and
then to match new, unfamiliar individuals to the template it has
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learned—for example, Dawkins' (1982) "armpit effect." Individuals that smell (or look or behave) like oneself or one's close kin
could be distinguished from those that smell (or look or behave)
differently. This mechanism would depend on the existence of a
strong correlation between genotype and phenotype.
Familiarity or association. Preferences may also depend on learning through social interaction. This may be the most common
means of kin recognition in nature. Individuals that are reared
together are more likely to be kin than nonkin.
Location. The fourth kin recognition mechanism depends on a
high correlation between an individual's location and kinship.
The rule states: "If it's in your nest, it's yours." Where an individual is and whom the individual encounters can also be based on
similar genes, for example, if parents exert discriminatory influence on where and with whom their offspring interact.
Kin Recognition in Animals
There is dramatic experimental evidence that many animal
species recognize genetic similarity. For example, bees block the
nest to prevent intruders from entering. In one study, bees bred for
14 different degrees of genealogical relationship were introduced
near nests (Greenberg 1979). There was a strong linear relationship
(r=0.93) between the ability to pass the guard bee and the degree
of genetic relatedness.
Mammals are also able to detect degrees of genetic relatedness
(reviewed in Fletcher and Michener 1987). For example, squirrels
produce litters that contain both sisters and half-sisters. Despite
the fact that they shared the same womb and inhabit the same
nest, full sisters fight less often than half-sisters, come to each
other's aid more, and are less prone to chase one another out of
their home territory. Recent experiments with squirrels demonstrate how rearing (together or apart) and relatedness (littermates
or non-littermates) affect juveniles' social interactions. Play-bout
frequencies were ordered (high to low): littermates reared
together > non-littermates reared together > littermates reared
apart > non-littermates reared apart. Statistical analysis revealed
that both rearing and relatedness contributed to this ordering
(Holmes 1995).
Genetic Similarity Theory
373
Similarity Recognition in Humans
In earlier papers, my colleagues and I extended the kin-selection
theory of altruism to the human case by proposing that, if a gene
can ensure its own survival by acting so as to bring about the
reproduction of family members with whom it shares copies, then
it can do so by benefiting any organism in which copies of itself
are to be found (Rushton, Russell and Wells 1984; Rushton 1989a).
Rather than merely protecting kin at the expense of strangers,
organisms might identify genetically similar others so as to exhibit
altruism toward these "strangers" as well as toward "kin." Kin
recognition would be just one form of genetic similarity detection.
Humans are capable of learning to distinguish kin from nonkin
at an early age. Infants can distinguish their mothers from other
women by voice alone at 24 hours of age, know the smell of their
mother's breast before they are 6 days of age, and recognize a photograph of their mother when they are 2 weeks old. Mothers are
also able to identify their infants by smell alone after a single exposure at 6 hours of age, and to recognize their infant's cry within 48
hours of birth.
Human kin preferences follow lines of genetic similarity. For
example, among the Ye'Kwana Indians of South America, the
words "brother" and "sister" cover four different categories ranging from individuals who share 50 percent of their distinctive
genes (identical by descent) to individuals who share only 12.5
percent of their genes. Hames (1979) has shown that the amount of
time the Ye'Kwana spend interacting with their biological relatives increases with their degree of relatedness, even though their
kinship terminology does not reflect this correspondence.
Anthropological data also show that in societies where certainty of paternity is relatively low, males direct material resources
to their sisters' offspring (to whom their relatedness is certain)
rather than to their wives' offspring (Kurland 1979). Paternity
uncertainty exerts other predictable consequences. Grandparents
spend 35 to 42 percent more time with their daughters' children
than with their sons' children (Smith 1981). Following bereavement, grandparents grieve more for their daughters' children than
for their sons' children (Littlefield and Rushton 1986). Family
members feel only 87 percent as close to the fathers' side of the
family as they do to the mothers' side (Russell and Wells 1987).
Finally, mothers of newborn children and her relatives spend
more time commenting on resemblances between the baby and
374 I I. Philippe Rushton
the putative father than they do about the resemblance between
the baby and the mother (Daly and Wilson 1982).
When the level of genetic similarity within a family is low, the
consequences can be serious. Children who are unrelated to a parent are at risk: a disproportionate number of battered babies are
stepchildren. Children of preschool age are 40 times more likely to
be assaulted if they are stepchildren than if they are biological
children (Daly and Wilson 1988). Unrelated people living together
are more likely to kill each other than are related people living
together. Converging evidence shows that adoptions are more
likely to be successful when the parents perceive the child as similar to them.
Mate Choice
A well-known phenomenon that is readily explained by genetic
similarity theory is positive assortative mating, that is, the tendency of spouses to be nonrandomly paired in the direction of
resembling each other (described in the introduction). This tendency even extends to socially undesirable characteristics, including aggressiveness, criminality, alcoholism, and psychiatric
disorders such as schizophrenia and the affective disorders.
Although alternative reasons can be proposed for this finding,
such as unsuccessful competition for the most attractive and
healthiest mates, it does suggest that the tendency to seek a similar partner may override considerations such as mate quality and
individual fitness.
A study of cross-racial marriages in Hawaii found more similarity in personality test scores among males and females who
married across ethnic groups than among those marrying within
them (Ahern, Cole, Johnson, and Wong 1981). The researchers
posit that, given the general tendency toward homogamy, couples
marrying heterogamously with respect to ethnicity tend to "make
up" for this dissimilarity by choosing spouses more similar to
themselves in other respects than do persons marrying within
their own ethnic group.
Assortative mating is found in taxa ranging from insects to
birds to primates, and it can be observed in the laboratory as well
as in nature (Fletcher and Michener 1987). Assortative mating also
occurs in plants (Willson and Burley 1983). To have evolved independently in such a wide variety of species, assortative mating
Genetic Similarity Theory I 375
must confer substantial advantage. Advantages thought to accrue
in human mates include (1) increased marital stability, (2)
increased relatedness to offspring, (3) increased within-family
altruism and (4) greater fecundity.
The upper limit on the fitness-enhancing effect of assortative
mating for similarity occurs with incest. Too much genetic similarity between mates increases the chances that harmful recessive
genes may combine. The negative effects of "inbreeding depression" have been demonstrated in many species, including
humans. As a result, the "incest taboo" has been hypothesized to
have an evolutionary basis, possibly mediated through negative
imprinting on intimate associates at an early age (van den Berghe
1983). Optimal fitness, then, may consist in selecting a mate
who is genetically similar but not actually a relative. Van den
Berghe (1983) speculates that the ideal percentage of relatedness
is 12.5 percent identical by descent, or the same as that between
first cousins.
Other animal species also avoid inbreeding. For example, several experiments have been carried out with Japanese quail, birds
that, although promiscuous, proved particularly sophisticated.
They preferred first cousins to third cousins, and both of these relatives to either unrelated birds or siblings, thus avoiding the dangers of too much or too little inbreeding (Bateson 1983).
I tested the hypothesis that human mating followed lines of
genetic similarity by examining blood antigen analyses from
nearly 1,000 cases of disputed paternity (Rushton 1988). Seven
polymorphic marker systems (ABO, Rhesus (Rh), MNSs, Kell,
Duffy (Fy), Kidd (Jk), and HLA) at 10 loci across six chromosomes
were examined in a sample limited to people of North European
appearance (judged by photographs kept for legal identifications).
These blood groups are sufficient to correctly identify more than
95 percent of cases in paternity disputes. They also reliably distinguish between fraternal twins. My results showed that genetic
similarity within pairs related to (1) whether the pair was sexually
interacting or randomly generated from the same sample, and (2)
whether the pair produced a child. Sexually interacting couples
shared about 50 percent of measured genetic markers, part way
between mothers and their offspring, who shared 73 percent, and
randomly paired individuals from the same sample, who shared
43 percent. Couples who produced a child together were 52 percent similar on this metric, whereas those who did not were only
44 percent similar (p<0.05).
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In other tests of the genetic similarity theory of assortative mating, studies show that mate choice is greater on the more heritable
of a set of homogeneous items. This prediction follows from theory because more heritable items better reflect the underlying
genotype. Examples of differing heritabilities used to establish the
theory include: for physical characters, 80 percent for mid-finger
length versus 50 percent for upper arm circumference; for intelligence, 80 percent for the general factor versus less than 50 percent
for specific abilities; for personality, 41 percent for having a preference for reading versus 20 percent for having many different
hobbies; and for attitudes, 51 percent for agreement with the death
penalty versus 25 percent for agreement with Bible truth. Thus,
Russell, Wells, and Rushton (1985) found spouses were more similar on the more heritable of 36 anthropometric variables, 5 perceptual judgment variables, and 11 personality variables. Rushton
and Russell (1985) found heritabilities predicted similarity
between spouses for 54 personality traits, 15 cognitive tests, and
13 anthropometric variables. Rushton and Nicholson (1988) found
that spouses were most similar on the more heritable of 15IQ subtests from the Hawaii Family Study of Cognition and 11 subtests
from the Wechsler Adult Intelligence Scale.
Intrafamilial Relationships
One consequence of genetic similarity between spouses is an
increase of within-family altruism. Several studies have shown
that not only the occurrence of relationships but also their degree
of happiness and stability can be predicted by the degree of
matching on personal attributes (reviewed in Rushton 1989a).
A related prediction can be made about parental care of offspring that differ in similarity. Sibling differences within families
have often been overlooked as a topic of research. Positive assortative mating makes some children genetically more similar to one
parent or sibling than to another. For example, if a father gives his
child 50 percent of his genes, 10 percent of which he shares with
the mother because of parental similarity, and the mother gives
the child 50 percent of her genes, 20 percent of which she shares
with the father because of parental similarity, then the child will
be 60 percent similar to the mother and 70 percent similar to
the father.
Genetic Similarity Theory I 377
Genetic similarity theory predicts that parents and siblings will
tend to favor those who are most similar. Littlefield and Rushton
(1986) tested this hypothesis in a study of bereavement following
the death of a child. Respondents picked which side of the family
the child "took after" more, their own or their spouse's. Spouses
agreed with each other 74 percent of the time on this question.
Both mothers and fathers grieved more intensely for children perceived as resembling their side of the family.
Other evidence of within-family preferences comes from a
review by Segal (1988) of feelings of closeness, cooperation, and
altruism in twin pairs. Compared with fraternal twins, identical
twins worked harder for their co-twins on tasks, maintained
greater physical proximity, expressed more affection, and suffered
greater loss following bereavement. Subsequently, Segal, Wilson,
Bouchard, and Gitlin (1995) found that degree of genetic relatedness predicted degree of bereavement and that the loss of a cotwin resulted in the same level of grief as the loss of a child or
a spouse.
A Genetic Basis for Friendship
Friendships also form on the basis of similarity, whether as perceived by the friends or for a variety of objectively measured characteristics, including activities, attitudes, needs, personality, and
anthropometric variables. Moreover, in the experimental literature on who likes whom and why, one of the most influential variables is perceived similarity. Apparent similarity of personality,
attitudes, or any of a wide range of beliefs has been found to
generate liking in subjects of varying ages and from many different cultures.
The tendency to choose similar others as friends is genetically
influenced. In a study of delinquency among 530 adolescent twins
by Rowe and Osgood (1984), path analysis revealed not only that
antisocial behavior was about 50 percent heritable, but that the
correlation of 0.56 between the delinquency of an individual and
the delinquency of his friends was mediated genetically. Adolescents genetically disposed to delinquency were genetically
inclined to seek each other out for friendship. In a study of 396
adolescent and young adult siblings from both adoptive and nonadoptive homes, Daniels and Plomin (1985) found that genetic
influences were implicated in choice of friends: biological siblings
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were more similar to each other in the types of friends they had
than were adoptive siblings.
In a study to examine similarity among male friendship pairs, I
used the same blood markers and differential heritabilities as in
my study of sexual partners. The best friends were 54 percent similar to each other using 10 loci from 7 polymorphic blood systems
(ABO, Rhesus (Rh), MNSs, P, Duffy (Fy), Kidd (Jk), and HLA). An
equal number of randomly chosen pairs from the same overall
sample were significantly less similar. Stratification effects were
unlikely because within-pair differences in age, education, and
occupation did not correlate with the blood similarity scores. Similarity between friends was strongest on the more heritable of 36
conservatism items and 81 personality items.
Independent corroboration that attitudes with high heritability
are stronger than those with low heritability has come from a
series of studies by Tesser (1993). Each subject responded "Agree"
or "Disagree" to attitudes with known heritabilities. Attitudes
higher in heritability were responded to more quickly, were more
resistant to change when attempts were made at social influence,
and were more predictive of liking of others who shared similar
attitudes. For example, similarity on more heritable attitudes correlated higher with attraction to a stranger imagined as a potential
friend, a romantic partner, and a spouse than did similarity on
less heritable items.
Epigenetic Rules in Social Development
Both the evolutionary and social sciences err in not making more
explicit that social learning is dependent upon the innate capacities and biases of the learner. For example, most models of cultural
transmission within the family (i.e., vertical, from parent to child,
and horizontal, from sibling to sibling) imply that siblings will
resemble each other, over and above shared genes, as a result of a
common family environment. An epigenetic model, in contrast, in
which genes incline individuals to acquire patterns of behavior
best fitting their particular genotype, leads to the expectation that
siblings will differ from each other. While it may seem intuitively
correct to assume that common family environment shapes individual development, consideration of data reveals quite a different set of relationships.
Genetic Similarity Theory I 379
Social development is guided by epigenetic rules that incline
individuals to particular learning experiences. As in the studies of
friendship formation among delinquents described in the last section, behavior genetic designs provide powerful tests of alternative hypotheses about the genetic and social influences on family
resemblances. Comparing 573 pairs of adult monozygotic and
dizygotic twins who had been reared together, Rushton, Fulker,
Neale, Nias, and Eysenck (1986) examined the cultural and genetic
inheritance of individual differences in altruism and aggression.
We found not only a strong association of genetic factors with the
characteristics in question but also a negligible influence of the
twins' shared environment. Rather, the distinct experiences of the
individual accounted for almost all the environmental influence.
The discovery that common family environment plays a very
limited role in social development (even for traits that parents are
expected to indoctrinate, such as altruism) runs counter to prevailing theories of personality development that assume that the
important environmental variance is between families, not within.
Yet the observation that the environmental factors that influence
development are those that are specific to each sibling, rather than
common, is robust, having been replicated using other research
designs (like adoption studies) and other social characteristics.
Regardless of whether one considers the transmission of socially
undesirable traits, such as crime, obesity, and schizophrenia, or
more normative personality characteristics, such as vocational
interests and value systems, the evidence reveals that whereas
genetic influences have an important role to play, the common
family environment alone has little apparent effect.
A compelling test of models of transmission has been made in
the context of social attitudes. Since attitudes are more flexible
than personality, purely cultural models of transmission might be
considered especially likely, with at least some vertical transmission occurring from parent to child. Yet in one compilation of
results, Eaves, Eysenck, and Martin (1989) showed that social scientists have typically misconceived the role of cultural inheritance
in attitude formation. Individuals acquire little from their social
environment that is incompatible with their genotype.
So far the discussion has been limited to individual social
development. However, the potential of epigenetic rules to bias
behavior and affect society goes well beyond ontogeny. Via cognitive phenotypes and group action, altruistic inclinations may be
amplified into charities and hospitals, creative and educative dis-
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positions into academies of learning, and martial tempers into
institutes of war. Such macrocultural innovations can be expected
to influence the genetic composition of future generations.
Ethnocentrism
The implications of the rinding that people moderate their behavior as a function of genetic similarity and epigenetic biases are farreaching. They suggest a biological basis for ethnocentrism.
Despite enormous variance within populations, it can be expected
that two individuals within an ethnic group will, on average, be
more similar to each other genetically than two individuals from
different ethnic groups. According to genetic similarity theory,
people can be expected to favor their own group over others.
Ethnic conflict and rivalry, of course, is one of the great themes
of historical and contemporary society. Local ethnic favoritism is
also displayed by group members who prefer to congregate in the
same area and to associate with each other in clubs and organizations. Understanding modern Africa, for example, is impossible
without understanding tribalism there. Many studies have found
that people are more likely to help members of their own race or
country than they are to help members of other races or foreigners, and that antagonism between classes and nations may be
greater when a racial element is involved.
Traditionally, political scientists and historians have seldom
considered intergroup conflict from an evolutionary standpoint.
That fear and mistrust of strangers may have biological origins,
however, is supported by evidence that animals often show fear
of and hostility toward strangers, even when no injury has ever
been received. Analogies may be drawn between the way monkeys and apes repel intruding strangers of the same species and
the way children attack another child who is perceived as being
an outsider.
Many of those who have considered nationalist and patriotic
sentiment from a sociobiological perspective, however, have
emphasized its apparent irrationality. Johnson (1986) formulated a
theory of patriotism in which indoctrination through socialization
and conditioning engage kin-recognition systems so that people
behave altruistically toward in-group members as though they
were genetically more similar than they actually are. In Johnson's
analysis, for example, patriotism may often be an ideology indoc-
Genetic Similarity Theory
I 381
trinated by the ruling class to induce the ruled to behave contrary
to their own genetic interests, while increasing the fitness of
the elite. He noted that patriotism is built by referring to the
homeland as the "motherland" or "fatherland," and that bonds
between people are strengthened by referring to them as "brothers" and "sisters."
According to genetic similarity theory, patriotism is more than
just "indoctrinated" altruism working to the individual's genetic
detriment. It is a strategy by which genes typically replicate copies
of themselves more effectively. The developmental processes that
Johnson (1986) and others have outlined undoubtedly occur, as do
other forms of manipulated altruism. However, if these were sufficient to explain the human propensity to feel strong moral obligation toward society, patriotism would remain an anomaly for
evolutionary biology. From the standpoint of optimization, one
might ask whether ethical systems would survive very long if
they consistently led to reductions in the inclusive fitness of those
believing in them.
If epigenetic rules do incline people toward constructing and
learning ideologies which increase their fitness, then patriotic
nationalism, religious zealotry, class conflict, and other forms of
ideological commitment can be seen as genetically influenced cultural choices that individuals make that, in turn, influence the
replication of their genes. Religious, political, and other ideological battles may become as heated as they do partly because of
implications for fitness; some genotypes may thrive more in one
ideological culture than in another. According to this view, Karl
Marx did not take the argument far enough: ideology serves more
than economic interest; it also serves genetic fitness.
Two sets of falsifiable propositions follow from this interpretation. First, individual differences in ideological preference are
partly heritable. Second, ideological belief increases genetic fitness. There is evidence to support both propositions. With respect
to the heritability of differences in ideological preference, it has
generally been assumed that political attitudes are mostly determined by the environment; however, as mentioned, both twin and
adoption studies reveal significant heritabilities for social and
political attitudes as well as for stylistic tendencies (Eaves,
Eysenck, and Martin 1989). Of course, no behavioral geneticist
believes that genes are 100 percent responsible for complex social
behavior. The battle is between those who believe 100 percent in
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environmental determinism and those who think that both genes
and environments affect behavior.
Examples of ideologies that increase genetic fitness include religious beliefs that regulate dietary habits, sexual practices, marital
customs, infant care, and childrearing (Reynolds and Tanner
1983). Amerindian tribes that believed it important to cook maize
with alkali had higher population densities and more complex
social organizations than tribes that did not, partly because cooking with alkali releases the most nutritious parts of the cereal,
enabling more people to grow to reproductive maturity (Katz,
Hodiger, and Valleroy 1974). The Amerindians did not know the
biochemical reasons for the benefits of alkali cooking, but their
cultural beliefs had evolved for good reason, enabling them to
replicate their genes more effectively than would otherwise have
been the case.
By the way of objection, it could be argued that although some
religious ideologies confer direct benefits on the extended family,
ideologies like patriotism decrease fitness (hence, most analyses of
patriotism rest on indoctrination and social manipulation).
Genetic similarity theory may provide a firmer basis for an evolutionary understanding of patriotism, for benefited genes do not
have to be only those residing in kin. Members of ethnic groups,
for example, often share the same ideologies, and many political
differences are genetic in origin. One possible test of genetic similarity theory in this context is to calculate degrees of genetic similarity among ideologues in order to examine whether ideological
"conservatives" are more homogeneous than the same ideology's
"liberals." Preserving the "purity" of an ideology might be an
attempt to preserve the "purity" of the gene pool.
Because ethnic conflict has defied explanation by the standard
social science disciplines, genetic similarity theory may represent
an advance in understanding. Eibl-Eibesfeldt (1989b) agreed with
me that if attraction toward similarity has a genetic component
then it provides a basis for xenophobia as an innate trait in human
beings. He reiterated that ethnocentrism is a phenomenon manifested in all cultures so far studied and presented his view that
generalized altruism began with maternal caretaking, a turning
point in the evolution of vertebrate social behavior, which up to
that time had been based on dominance and submission. The
mother-child bond established the possibility of gradients in
familiarity-trust/strangeness-suspicion.
Gt'Mi'fi'c Similarity Theory
I 383
Van den Berghe (1989) also endorsed the genetic similarity perspective, stating that ethnicity had a "primordial dimension." In
his 1981 book, The Ethnic Phenomenon, he had suggested that ethnocentrism was a case of extended nepotism, with even relatively
open and assimilative ethnic groups policing their ethnic boundaries against invasion by strangers by using badges as markers of
group membership. These were likely to be cultural rather than
physical, he argued, such as linguistic accent or clothing style.
Now, it seemed to him (van den Berghe 1989), identifying fellow
ethnics using shared traits of high heritability provided a more
reliable method than cultural, flexible ones, although these other
membership badges could also be used.
Adopting a gene-based evolutionary perspective for ethnic
conflict may prove illuminating, especially in the light of the conspicuous failures of environmentalist theories. With the breakup
of the Soviet bloc, many Western analysts have been surprised at
the outbreak of the fierce ethnic antagonisms long thought over.
Lynn (1989,534) put it directly:
Racial and ethnic conflict is occurring throughout the world—between
Blacks and Whites in the United States, South Africa, and Britain;
Basques and Spaniards in Spain; and Irish and British in Northern Ireland. These conflicts have defied explanations by the disciplines of
sociology, psychology, and economics... genetic similarity theory represents a major advance in the understanding of these conflicts.
Lynn (1989) raised the question of why people remain as irrationally attached as they do to languages, even almost dead ones
such as Gaelic and Welsh. One function of language barriers, he
suggested, was to promote inbreeding among fellow ethnics. The
close mapping recently found to occur between linguistic and
genetic trees is compatible with Lynn's hypothesis. Cavalli-Sforza,
Menozzi, and Piazza (1994) combined 120 allele frequencies from
42 populations into a phylogenetic tree based on genetic distances
and related it to a taxonomy of 17 linguistic phyla. Despite the
apparent volatility of language and its capacity to be imposed by
conquerors at will, considerable parallelism between genetic and
linguistic evolution was found.
The theoretical stance taken so far predicts that the ease of producing patriotic sentiment and internal harmony varies with the
genetic homogeneity of the national group. As van den Berghe
(1981,27) put it: "Ethnicity can be manipulated but not manufactured." Since ethnic aspirations are rarely justified in terms of
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naked genetic self-interest, any analysis will necessarily have to be
conducted at a deeper level than surface ideology. Political interests are typically couched in the highest of ethical terms, no matter how utilitarian, transparent, or heinous these appear to
opponents.
Genetic similarity is only one of many possible influences operating on political alliances. Obviously, causation is complex, and it
is not intended to reduce relationships between ethnic groups to a
single cause. Fellow ethnics will not always stick together, nor is
conflict inevitable between groups any more than it is between
genetically distinct individuals. As indicated, people can be
manipulated into working for "other groups." People also work
for other motives, such as economic success as well as reproductive success. However, as van den Berghe (1981) pointed out, from
an evolutionary perspective, the ultimate measure of human success is not production, but reproduction.
While cultural evolution and organic evolution are undoubtedly different, they are linked reciprocally in complicated ways
and seem to share certain properties. Both appear to "strive" to
replicate their units, if necessary at the expense of the other system's units (alleles in the case of organic evolution; "memes" or
"culturgens" in the case of cultural evolution). Their seat of battle
is the individual human mind, which only dimly perceives the
consequences of its choices, based as they are on many competing
elements. Thus, ideologies can arise which have the paradoxical
effect of dramatically decreasing fitness. A classic example of such
a lethal culturgen is found among the Shakers, a religious sect
which considers sex to be so sinful that it imposes celibacy upon
even its married members. This ideology has nonetheless been
quite successful in replicating itself through several generation,
new adherents being recruited, largely via adoptions. The members' genes, of course, fail to replicate.
Selection of Groups
Humans have obviously been selected to live in groups. Typically,
they hold a territory in common that they fill with symbols of their
group and that they are willing to defend (Eibl-Eibesfeldt 1989a).
The line of argument presented so far may have implications for
determining whether group selection occurs among humans.
Although the idea of group selection, defined as "selection that
Cciwtic Similarity Tlicoru I 385
operates on two or more members of a lineage group as a unit" (E.
O. Wilson 1975,585) was popular with Darwin, Spencer, and others, in recent decades it has often been thought not to play a major
role in evolution. Hamilton's (1964) theory of inclusive fitness, for
example, has been typically regarded as an extension of individual selection, not group selection (Dawkins 1976; 1982).
Group selection was brought to center stage by WynneEdwards (1962) in the context of altruism. He suggested that
whole groups of animals collectively refrained from overbreeding
when the density of population became too great, even to the
point of killing their offspring. Such self-restraint, he argued, protected the animals' resource base and gave them an advantage
over groups that did not practice restraint and became extinct as a
result of their profligacy. This extreme form of the group selection
claim was immediately disputed, and a great deal of argument
and data was marshaled against the idea (Williams 1966). There
did not seem to exist a mechanism (other than favoring kin) by
which altruistic individuals could leave more genes than selfish
individuals who cheated.
A compromise was offered by E. O. Wilson (1975), who suggested that although genes are the units of replication, their selection could take place through competition at both the individual
and the group levels; for some purposes these can be viewed as
opposite ends of a continuum of nested, ever enlarging sets of
socially interacting individuals. Kin selection is thus seen as intermediate between individual and group selection. Group selection
may have been prematurely rejected due to a failure to see that
with genes as "replicators," it is irrelevant whether it is individuals, social groups, or still higher-level entities that are the "vehicles" of selection (for an extended discussion see D. S. Wilson and
Sober 1994).
Among humans, genetic similarity theory makes group selection especially likely because altruism is conferred beyond immediate kin. Through language, law, religious imagery, and patriotic
nationalism, all replete with kin terminology, ideological commitment extends altruistic behavior enormously. Groups made up of
people genetically disposed toward honesty, trust, temperance,
willingness to share, loyalty, and self-sacrifice will have a distinct
genetic advantage over groups that do not have this makeup. In
addition, if strong socialization pressures, including "mutual
monitoring" and "moralistic aggression," are used to shape values
386 I /. Philippe Rushton
within the group, a mechanism is provided for controlling, and
even removing, the genes of cheaters.
As indicated, social learning is genetically biased. Social psychological studies of cultural transmission show that people pick up
trends more readily from role models who are similar. It is likely
that different ethnic groups leam from different trendsetters and
that the variance among groups is increased, thereby increasing the
efficacy of group selection. Those groups adopting an optimum
degree of ethnocentric ideology may have replicated their genes
more successfully than those that did not. Evolution under bioculrurally driven group selection, including migration, war, and genocide, may account for a substantial amount of change in human
gene frequencies. E. O. Wilson (1975,573-74) put it forcefully:
If any social predatory mammal attains a certain level of intelligence,
as the early hominids, being large primates, were especially predisposed to do, one band would have the capacity to consciously ponder
the significance of adjacent social groups and to deal with them in an
intelligent organized fashion. A band might then dispose of a neighboring band, appropriate its territory, and increase its own genetic representation in the metapopulation, retaining the tribal memory of this
successful episode, repeating it, increasing the geographic range of its
occurrence, and quickly spreading its influence still further in the
metapopulation. Such primitive cultural capacity would be permitted
by the possession of certain genes.... The only combination of genes
able to confer superior fitness in contention with genocidal aggressors
would be those that produce either a more effective technique of
aggression or else the capacity to preempt genocide by some form of
pacific maneuvering. Either probably entails mental and cultural
advance. In addition to being autocatalytic, such evolution has the
interesting property of requiring a selection episode only very occasionally in order to proceed as swiftly as individual-level selection. By
current theory, genocide or genosorprion strongly favoring the aggressor need take place only once every few generations to direct evolution. This alone could push truly altruistic genes to a high frequency
within the bands.
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